in cycles of 11 years. During sun-spot activity eruptive prominences rise to heights of many thousands of miles and streams of electrons are shot forth with such force that they may possibly even penetrate deeply into our own atmosphere causing disturbances such as magnetic storms and auroras._-_figure_135.jpg)
SUN-SPOTS.
The earth is so small compared with the huge bulk of the sun that it would be lost in one
of these "spots." Photograph by the Mount Wilson Observatory. If a total solar eclipse occurs at a time when these great magnetic storms are raging in particular fury on the sun's surface, the corona always appears brighter and more intricate than when the sun is peaceful.
Sun-spots were very numerous in 1915 and 1916. The next spot maximum will occur about 1926, then in 1937 and so on. For three years or four years they appear with great frequency, then declining to a minimum for three or four years, rise to a
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